1. Field of the Invention
This invention relates to an air bag apparatus as a supplemental restraint system for a vehicle, and, more particularly, to a side air bag apparatus having an air bag unit installed within a seat.
2. Description of Related Art
An air bag apparatus, which typically has an air bag unit installed in the inside of a steering wheel, automatically serves as a supplemental restraint system to protect a driver sitting in the driver's seat and fastened by a seat belt upon an occurrence of a frontal collision. In recent years, in order to protect drivers and/or passengers against side collision, it is becoming widespread to provide a side air bag apparatus with an air bag unit installed at one side of a seat. Such a side air bag apparatus is known from, for example, Japanese Unexamined Patent Publication No. 6-64491.
In order to ensure stiffness and rigidity of a seat, the seat is typically encircled and reinforced by a metal frame. In cases where an air bag unit is placed within one side of the seat, because the air bag unit is surrounded by a cushioning pad, the air bag unit encounters deformation or is possibly damaged when, for example, the seat at its opposite sides is held by a robot and installed to a vehicle. Further, when a person puts a cargo into the vehicle, the seat at its side is possibly hit by the cargo. In that point of view, the air bag unit needs improved protection against an external lateral impact. Some of side air bag apparatuses have an air bag unit attached to the seatback frame from the outside. Such a side air bag apparatus is known from, for example, Japanese Unexamined Patent Publication No. 8-242967.